Elevation is a stronger predictor of morphological trait divergence than competition in a radiation of tropical lizards

• Published in: The Journal of animal ecology 2021-04, Vol.90 (4), p.917-930
• Main Authors: Slavenko, Alex, Allison, Allen, Meiri, Shai, White, Hannah
• Format: Article
• Language: English
• Subjects: Adaptation; Animals; character displacement; Climate; Competition; competitive exclusion; Divergence; Ecological effects; Ecosystem; Elevation; elevational gradient; Habitat utilization; Harsh environments; Islands; Lizards; Mathematical analysis; Microenvironments; Microhabitats; Morphology; mountains; niche partitioning; Occupancy; Papua New Guinea; Partitioning; Phenotype; Radiation; Scincidae; Species richness; Sympatric populations; Sympatry; Thermoregulation; tropical ecology
• ISSN: 0021-8790; 1365-2656
• DOI: 10.1111/1365-2656.13420

Adaptations for efficient performance are expected to shape animal morphology based on selection for microhabitat use and ecological forces. The presence of competitor species is predicted to cause niches to contract and enhance trait divergence. Therefore, increased species richness is expected to lead to greater trait divergence, and to result in reduced overlap and similarity between morphologies of sympatric species. We examined patterns of morphospace occupancy and partitioning in the skink fauna of New Guinea, the world's largest tropical island. Because skink species richness is largely decoupled from elevation in New Guinea, we could examine the effects of both factors (as proxies for competition and abiotic conditions), on morphospace occupancy and partitioning. We measured 1,860 specimens from 79 species of skinks throughout Papua New Guinea, and examined their morphospace occupancy in a spatial context. We calculated, for each assemblage within equal‐area cells, the volume of morphospace occupied by all skinks, the mean volume occupied per species, and the mean distance and overlap between all species pairs. We then examined whether these metrics are related to species richness and elevation. Elevation is a stronger predictor of morphospace occupancy than species richness. As elevation increases, intraspecific variation decreases and morphologies become more similar to each other such that overall morphospace occupancy decreases. Highland skinks are, on average, smaller, thinner and shorter limbed than lowland species. We hypothesise that harsh climates in the New Guinea highland habitats impose strong selection on skinks to occupy specific areas of morphospace that facilitate efficient thermoregulation in suboptimal thermal conditions. We conclude that the effect of competition on trait divergence on a community and assemblage scale is eclipsed by abiotic selection pressures in these harsh environments. The authors provide a large‐scale examination of morphological trait divergence in a radiation of tropical lizards. They show that, for Papua New Guinea skinks, morphological trait divergence is not governed by competition, as classical ecological theory predicts. Rather, morphologies likely represent selection to different environmental conditions across New Guinea's mountain ranges.